Typically completions involve running in casing or hanging a liner and cementing it into position in the wellbore. Before running in a perforating gun the wellbore is generally circulated clean with brine so that the well is reasonably free of debris before the guns are set off. This circulation process can take days and is quite costly. Beyond that the casing or liner that is run in and cemented limits the gun size that can be run through it and that, in turn, limits the shot density in the gun.
If a tube or passage, of sufficient cross sectional area to deliver cement to the borehole below the gun, were placed inside the gun, the space it occupied would restrict the volume available for perforating charges. This would compromise the quality of the perforations and thereby the well performance would be degraded.
Existing techniques of perforating through cemented casing or liner or dealing with other aspects of perforating gun design can be seen in U.S. Pat. Nos. 2,669,928; 4,637,468; 7,000,699; 7,114,564; 7,195,066.
The present invention seeks to avoid the design constraints of prior systems by delivering a gun or guns below a tubular that is supported off existing casing with a hanger. The cement, or other fluid or material for hydraulic isolation and mechanical support, is first delivered in open hole and is formulated to allow enough time to run in with the gun or guns below a liner that has a hanger associated with it. The gun and liner displace cement to the annular space around the liner and preferably below the hanger. The gun or guns are fired once the surrounding cement or other fluid or material has set. The gun may be larger than in prior designs because the cemented liner in which the gun had to be advanced is no longer there. Furthermore, cleaning the debris from the well with circulation of brine can now be limited to the region above the hanger and doesn't need to extend deeper to where the gun or guns will be positioned when shot. These and other advantages of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while understanding that the full scope of the invention is given by the appended claims.